Enamel matrix serine proteinase 1 (EMSP1) is proposed to process enamel proteins during the secretory stage, and degrade enamel proteins during the early maturation stage of amelogenesis. EMSP1 is believed to be critical for proper dental enamel formation and defects in the human EMSP1 gene are suspected of causing amelogenesis imperfecta. Two hypotheses are tested: l. EMSP1 function is essential for the correct processing of enamel matrix proteins during the secretory stage of enamel formation, and that a loss of function can result in hypoplastic enamel. 2. EMSP1 function is essential for the degradation of enamel matrix proteins during the transition/early maturation stages of enamel formation, and that a loss of function can result in hypommeralized enamel. The following 4 Specific.Aims are proposed to test these hypotheses: l. To determine the temporal and spatial expression of EMSP1 during the secretory. transition. and maturation stages of enamel biomineralization. In situ hybridization and immunohistochemistry will be performed on mouse maxillae and mandibles. The first and second molars and incisors will be analyzed from newborn, postnatal (PN) days 2, 4, 6, 8 and 14 and adult. 2. To characterize the enzymatic activity of EMSP1 on amelogenin. Recombinant pig amelogenin will be digested by recombinant pig EMSP1 in vitro. The digestion products will be characterized by Edman degradation and mass spectrometry and compared to amelogenin cleavage sites that occur in vivo. 3. To characterize enamel formation in the absence of mouse EMSP1 expression. EMSP1 knock-out mice will be generated and characterized. 4. To determine the genetic linkage of the human EMSP1 gene with inherited defects of dental enamel formation. In collaboration with 3 laboratories that have assembled large numbers of kindreds suffering for amelogenesis imperfecta (AI), a candidate gene approach will be used to establish linkage between the human EMSP1 gene and AI . Accomplishing these aims will gain important insights into the action of EMSP1 in the organization, processing, turnover, and degradation of enamel matrix proteins during enamel biomineralization.